Free-form catadioptric illumination lens

Abstract

An illumination lens for hemispherically emitting light emitting diodes is disclosed that produces a square illumination pattern too narrow for a refractive lens to produce by itself. The lens is freeform in that it departs from circular symmetry in order to produce a square pattern. It is catadioptric in that it comprises a central refractive lens with a square output of desired angular width and a surrounding TIR prism that produces the same square output, overlapping the first for better uniformity of the sum. The central lens and circumambient TIR prism are joined in a monolithic configuration suitable for injection molding. Vector equations are disclosed for generating the shapes of the five optically active surfaces of the invention, two internal surfaces forming a central cavity surrounding the LED and three external surfaces, all five departing from circular symmetry.

I claim: 
     
       1. A dual free-form lens for producing illumination patterns having corners using a hemispherical light pattern-emitting LED, comprising:
 a central refractive lens intercepting approximately one half of the hemispherical light pattern, from a central axis outward to a predetermined angle; 
 an annular total internal reflection prism surrounding the central refractive lens, intercepting the hemispherical light pattern beyond the predetermined angle; 
 the central refractive lens and the total internal reflection prism forming a cavity for receiving the LED; 
 wherein the central refractive lens and the total internal reflection prism produce two substantially overlapping illumination patterns; and 
 wherein surface distortions in the central refractive lens and the total internal reflection prism spread light azimuthally toward the corners of the illumination patterns. 
 
     
     
       2. The dual free-form lens of  claim 1  wherein the surface distortions occur on portions of the dual free-form lens facing the cavity. 
     
     
       3. The dual free-form lens of  claim 1  wherein portions of the dual free-form lens outside the cavity are rotationally symmetric. 
     
     
       4. The dual free-form lens of  claim 1  wherein the central refractive lens and the total internal reflection prism share a common edge ray angle. 
     
     
       5. The dual free-form lens of  claim 1  wherein the LED emits a supra-Lambertian cumulative light distribution. 
     
     
       6. The dual free-form lens of  claim 1  wherein the predetermined angle comprises an edge ray angle substantially at 50% of the LED's total output. 
     
     
       7. The dual free-form lens of  claim 1  wherein the total internal reflection prism includes a developable lateral outer surface of slightly varying tilt. 
     
     
       8. The dual free-form lens of  claim 1  wherein the total internal reflection prism includes a refractive cone having a non-circular perimeter. 
     
     
       9. The dual free-form lens of  claim 1  wherein the total internal reflection prism is mirror-symmetrical about its axes and diagonals, thereby having free-form coordinates in repetitions of 0-45 degrees for producing a square illumination pattern. 
     
     
       10. The dual free-form lens of  claim 1  wherein the central refractive lens and the total internal reflection prism deflect central LED light rays to render the illumination pattern annular with a darkened center. 
     
     
       11. The dual free-form lens of  claim 1  further comprising an annular base at an intersection of the total internal reflection prism and the cavity. 
     
     
       12. The dual free-form lens of  claim 11  further including mounting legs protruding from the annular base. 
     
     
       13. A monolithic optical element for producing a square illumination pattern from a hemispherical light pattern-emitting LED, comprising:
 an interior cavity defined by a circular free-form surface and a quasi-conical lateral interior surface, the lateral interior surface leaning more horizontally on a diagonal of the square illumination pattern; 
 the circular free-form surface and an exterior hemispherical surface defining a central refractive lens; 
 the lateral interior surface, together with an upper conical surface and a quasi-conic total internal reflection surface, forming an internal reflection prism; and 
 wherein the central refractive lens and the total internal reflection prism spread light azimuthally toward corners of the square illumination pattern, thereby creating substantially overlapping square illumination patterns of uniform light distribution. 
 
     
     
       14. The element of  claim 13  wherein the quasi-conical lateral interior surface is mirror-symmetrical about its axes and its diagonals. 
     
     
       15. The element of  claim 13  wherein the quasi-conical lateral interior surface has a local tilt angle adjusted point-to-point from vertical as it enters the total internal reflection prism. 
     
     
       16. The element of  claim 13  wherein the upper conical surface and a quasi-conic total internal reflection surface have straight line profiles. 
     
     
       17. The element of  claim 13  wherein the internal reflection prism has a non-circular perimeter.